The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
Superconducting electronics, primarily involving Josephson junctions and related devices have been crucial in several analog and digital electronic applications, as well as in quantum computing. With the report of Josephson junctions (JJ), it was quickly realized that these devices can be used advantageously as significantly fast switches and logic devices compared to conventional CMOS based logic [1-3]. A voltage-state type logic was pursued in earlier developments at IBM, for example, which used zero-voltage of JJs during its superconducting state as logical ‘0’ and corresponding non-zero voltage of its normal state as logical ‘1’ [5]. This logic family found difficulty competing with CMOS logic due to several disadvantages including poor choice of superconducting materials, and mainly, the use of under-damped Josephson junctions that latch into the voltage state, once switched [6], although several improvements were suggested [7, 8]. Some of the drawbacks of a voltage-state logic family were addressed using single flux quantum (SFQ) logic, which employs over-damped JJs, was introduced in 1985 [9] and was experimentally demonstrated in 1987 [10]. Later, several improvements were suggested for circuits in this logic family [11-13].
Rapid single-flux-quantum (RSFQ) logic family is known to perform arithmetic and logic operations at compellingly high clock speeds (a few hundred GHz) [14, 15] using significantly lower energy compared to existing CMOS technologies [17-19]. The basic logic elements of this technology employ superconducting loops, broken with JJs, that store flux quanta as its basic logic element. The state of the element can be measured as voltage pulses with quantized area [6]. However, RSFQ logic has disadvantages in having static power dissipation and in requiring relatively large DC current biases to supply current to all the junctions, which, in-turn, introduce difficulties in design. These two disadvantages were overcome by other related technologies that use the same quantized flux logic but with improved biasing techniques such as low voltage RSFQ [19, 20], energy-efficient RSFQ (ERSFQ/eSFQ) [17, 18, 21], reciprocal quantum logic (RQL) [22, 23] and adiabatic quantum flux parametron (AQFP) [24, 25].
Quantum phase-slip is a phenomenon in superconducting systems where the phase difference between two connected superconducting regions changes by 2π with the suppression of the superconducting order parameter to zero. This occurs with quantum tunneling of vortices or fluxons across a narrow superconducting line, which is a dual to macroscopic quantum tunneling of charges across the insulating barrier in Josephson junction structures [26]. These effects have been studied extensively for quasi-one-dimensional nanowires, with thermally induced phase slips observed near the superconducting transition temperatures of the nano-wire and quantum phase-slips at significantly lower temperatures [39-46]. Qubits based on coherent quantum phase-slips were proposed [45] and coherent phase-slip events were observed [44].
QPSJ-based structures may serve as a potential circuit element in applications in superconducting electronics, quantum information processing and as a current standard. However, demonstrating a QPSJ with proper DC and RF operation has been relatively challenging to implement practically [46]. There has been no platform to identify potential applications of a QPSJ in electronic circuits.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.